Adverb (fukushi), Adverb taking the 'to' particle, Suru verb
hanging around; wandering around (aimlessly); moving around (restlessly); running around
Onomatopoeic or mimetic word
電車の中を子供がウロチョロしていて不愉快だった。I felt uncomfortable with those kids loitering around in the train.
Also written ウロチョロ